1. Field of the Invention
The present invention relates to a developing apparatus for a copier, facsimile apparatus, printer, or other similar image forming apparatus that uses an electrophotographic process, and also to a process cartridge comprising this developing apparatus.
2. Description of the Background Art
In the image forming apparatus, such as a copier, printer, or facsimile apparatus, which uses the electrophotographic process, it is important particularly to supply a developer to a development region between a photosensitive body and a developing sleeve in order to stably obtain, for long periods, a high-quality image with a good graininess of a halftone image, with the satisfied image density, and with no defects such as contamination of the surface. The amount of the developer supplied, i.e., the amount of the developer to be drawn, to the development region is set by a magnetic force of a magnetic roller inside the developing sleeve, as well as by the distance (doctor gap) between the developing sleeve and a developer amount regulating member (doctor blade). However, the amount often fluctuates over time due to change of the developer, which is caused because the developer constantly undergoes a stress generated from the doctor blade by repeated copying. Especially the drawn amount is reduced over time, which causes on an image a problem, such as an insufficient image density or traces of the carrier ear, and consequently the apparatus wears out.
In Japanese Patent Application Laid-Open No. 2000-47489, for example, the magnetic force distribution of a magnetic roller which acts as magnetic field generating means and is in the developing sleeve is optimized in order to stabilize, for long periods, the amount of the developer to be drawn; however, it is not taken into consideration that the condition of the developer changes because of repeated coping, thus it is understood that the effect of the optimization is not enough to stabilize the amount of the developer to be drawn.